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Subsurface Characterization of a Quick-Clay Vulnerable Area Using Near-Surface Geophysics and Hydrological Modelling
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0002-7020-8769
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0003-1241-2988
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.ORCID iD: 0000-0002-6257-3088
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Physical geography, Stockholm University.ORCID iD: 0000-0002-2261-4279
2019 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 10, no 5, p. 1685-1705Article in journal (Refereed) Published
Abstract [en]

Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 ms-1 and resistivity from approximately 80 to 100 Ωm) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow–outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.

Place, publisher, year, edition, pages
2019. Vol. 10, no 5, p. 1685-1705
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-375560DOI: 10.5194/se-10-1685-2019ISI: 000489879100001OAI: oai:DiVA.org:uu-375560DiVA, id: diva2:1286829
Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-11-08Bibliographically approved
In thesis
1. Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
Open this publication in new window or tab >>Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quick-clay landslides are considered one of the most important geohazards in Sweden, Norway, and Canada. The deposits involved are glacial and postglacial clays and silty clays, which are very sensitive to increased stress that may collapse their structure and cause liquefaction.

A multidisciplinary approach was adopted in this study of quick clays in an area of southwest Sweden that is prone to landslides. It was mainly based on geophysical methods, but was complemented and validated with geotechnical, geological, and hydrological data. Downhole geophysics, land and river reflection seismics, radio magnetotellurics, P-wave refraction tomography, magnetics, and multichannel analysis of surface waves comprised the main geophysical methods used in this research. Laboratory measurements of core samples, such as grain size analysis, mineral magnetic properties, fossil content, X-ray fluorescence, cation exchange capacity, X-ray powder diffraction, electrical conductivity, and pH were also taken. Hydrological modelling was used to obtain information on the properties of groundwater within a coarse-grained layer, given the importance of this information in the formation of quick clays.

The evaluation of the physico-chemical properties of the coarse-grained layer revealed high values of magnetic susceptibility, probably as a result of fluvial sorting, which tends to accumulate denser minerals such as magnetite. Potential quick clays were visually observed above this layer, and their presence was also confirmed by geotechnical data acquired in previous studies. Marine fossils identified within the coarse-grained layer confirmed the glaciomarine origin of the clays. Geophysical results revealed the presence of large-scale structures, an undulating fractured bedrock and a coarse-grained layer sandwiched between clay deposits, with leached sediments on top and unleached sediments below. This layer, important for the development of quick clays in the area, was 3D modelled in a regional context. Magnetic data also revealed that the coarse-grained layer together with quick clays, have the potential to act as a sliding prone layer. Multichannel analysis of surface waves helped to geotechnically characterize the area. Although the results could not reach the deeper layers, it did yield information about the shallower layers of clay, silt and sand. The VS30 values indicated the presence of soft soils, as well as soft clays/silts with high plasticity index and high water content.

This PhD is expected to improve the current knowledge of quick-clay landslides and how they are preconditioned. Climate change will probably affect the study area in the near future, most likely increasing landslide risk, therefore, research should continue and advance to new levels. Application of other geophysical methods such as borehole or geophysical monitoring, and induced polarization, could provide more information about the formation of quick clays and associated landslides.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1775
Keywords
Quick-clay, reflection seismic, landslide, southwest Sweden, borehole logging, physico-chemical properties, hydrogeological modelling, multichannel analysis of surface waves, magnetics
National Category
Geophysics Geosciences, Multidisciplinary Geology Environmental Sciences
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-375568 (URN)978-91-513-0575-2 (ISBN)
Public defence
2019-03-29, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-03-05 Created: 2019-02-11 Last updated: 2019-03-18

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